Method for rendering leather water repellent



Patented May 18, 1954 UNITED -METHOD FOR -RENDERIN G HEATHER WATER REPELLENT 'Toivo A. Kauppi, Midland, Mich, assignor to'Dow Corning Corporation, Midland, Mich a corporation ofMichigan NoDrawing. Application February 21,1951, Serial-No. 212,260

40laims. (C1. 117--135.5)

This invention relates to leather containing asiloxane.

'There has long been a need "for a material which when incorporatedin l'eather'would render thematerial'water repellent without clogging the pores thereof. It is also desirable that such a material should not change the 'basiccharacteristics of the leather, such as ease'of polishing, colorand texture.

It isan object of this invention to produce a leather composition which is impervious in water under severe conditions; Another object is to provide a leather which maybe employed in shoes and which willrender them waterrepellent'without affecting the'appearance. Another object is to provide a leather composition which is not deteriorated byoil. Other objects and advantages will be apparent from the following description.

'In-the past, many attempts have'b-een made to adapt'siloxanes for use in'leather articles. These attempts did not meet with pr'actica'lsuccess-because the'treated leather showed little or no improvement in such properties as forexample, water repellency, over leather which had been impregnated 'with organic -material conven tionally used with leather. One of "thechief deficiencies was the inability to prevent penetration of water through the leather when it was stretched and/or flexed. This fatal defect in siloxanetreated leather has been remedied by the present invention.

This invention relates to a composition of matter composed of "leather containing-from 0.1 to 6d per cent by weight based upon theweight of the leather of a methylsiloxane composed of trimethylsiloxane units and SiOz units in such proportions that the ratio of methyl radicals to siliconatoms is from 1 to 2.5.

The applicant has discovere'd'that when'leather is impregnated with the particular siloxanes above defined in the amounts specified, a different order of water repellency is obtained from that produced by any other known organosilicon material.

The leather is best treated by contacting it with a solution of the siloxane in a volatile solvent. The leather may be contacted either by swabbing it with the solution or by immersing it in the solution and agitating the leather. The latter method is the preferred form of treatment.

For best results, the concentration of the solutions should be from 1 to 50 per cent by weight siloxane. Optimum water repellency is obtained at a concentration of 25 per cent but other concentrations may be preferable for other optimum 2 values such as for example, oil'resista'nce. After impregnation is completed, the leather is removedfrom contact with the solution and airdried.

Any type leather whether tanned, tawed or otherwise'cured, is within the scope of the present invention. The leather may be untreated or "it may contain any of theadditives normally emplcyed'with leathers, such as dyes; oils, greases or fats.

The siloxanes employed herein are'copolymers composed essentially of "trimethylsiloxane units and unsubstituted 'sil'oxane unitsThey may be prepared by cohydrolysis of a silane of the formula (CH3)3SiX, where X isany'hydrolyzable group, with silicon tetrahalides or silicon tetraalkoxides. The cohydrolysis-is carried out in the usualma'nner. Alternatively, the copolymer may be prepared by reacting trimethylchlorosilane, trimethylalkoxysilanes or hexamethyldisiloxane with asilica sol'under acid conditions. Thezlatter method is more particularly-set forthin the copending application of William H. Daudt and Leslie Tyler, Serial No. l8,720, filed-Septemher 13, 1950, and assignedto the assignee'of this invention.

If desired, the above defined copolyzner may .bemixed with up to 50 percent by weight, but no more, of other 1 organosilicon materials. Materials which may bemixed with the copolymer are organosiloxanes in which the organic radicals are any monovalent hydrocarbon radical or organopolysilanescontaining Si--Si linkages in which the organic radicals are any monovalent hydrocarbon radical. Specific examples of such additives are dimethylsiloxane fluids, methylphenylsiloxane r e sin s, methylphenylsiloxane fluids, stearyl silsesquioxane, buty1methylpolysilane, phenylmethylpolysilane a n d stearylmethyipolysilane. Obviously, "any of the above materials must be in a soluble form.

Solvents which may be employed in this invention are petroleum hydrocarbons, benzene, toluene and Xylene.

One use for the present invention is in conjunction with shoes. The solution of the siloxane may be applied to the surface thereof and dried. The shoes become water repellent so that overshoes may in most cases be dispensed with. The treatment does not interfere with polishing the shoes.

The water repellency of the leather was meas-- ured in the following manner. A strip of leather was clamped between a fixed and moving arm. The leather was placed grain side up and at the maximum separation of the arms, the leather was under a five pound tension. The flexing arm in closed position was one inch from the fixed mount and moved a total distance of 2% inches. The unit operated at 40 cycles per minute. The movement of the unit gave a rapid flexing and stretching action to the test sample. Before the action was started, a drop of water was placed on the grain side of the leather. The test was continued until the water had penetrated to the flesh side.

By employing this method, leather which was not impregnated with the siloxane was penetrated by the water in 500 to 650 flexes.

The following examples are illustrative only and should not be construed as limiting the scope of the invention. The scope is properly set forth in the appended claims.

Example 1 and air-dried. It was placed on the flexing machine and a drop of water put on the grain side. It required 5,000 flexes before water seeped through the leather. By comparison, the same leather which had not been treated with the siloxane was penetrated by the water in about 550 flexes.

Example 2 A siloxane composed of 70 per cent of copolymeric siloxane of Example 1 and 30 per cent by weight of a dimethylsiloxane fluid was dissolved in a petroleum distillate so as to give a per cent by weight solution based on the total siloxane. A piece of treated leather different from that of Example 1 was immersed in this solution and agitated for five minutes. The leather was removed and air-dried and it required 10,500 flexes before water would penetrate from the grain to the flesh side. By contrast, a sample of the same piece of leather which was not treated with siloxane was wet through at 650 flexes.

Example 3 The procedure of Example 1 was repeated except that the siloxane employed was 70 per cent of the siloxane in Example 1 and per cent monostearylsiloxane. The resulting leather withstood 8,500 flexes before the water penetrated.

cept that the siloxane was a mixture of per cent of the copolymer of Example 1 and 30 per cent of stearylmethylpolysilane. The treated leather required 3,000 flexes before it wet through.

Example 5 The procedure of Example 1 was repeated except that the siloxane employed was '70 per cent by weight the siloxane of Example 1 and 30 per cent by weight of a copolymeric phenylmethylsiloxane fluid. The resulting leather withstood 4,000 flexes before water penetrated.

That which is claimed is:

l. The method of rendering leather water repellent comprising contacting the leather with a solution of a methylpolysiloxane composed of trimethylsiloxane units and S102 units in such proportion that the ratio of methyl radicals to silicon atoms is from 1 to 2.5, said solution containing from 1 to 50 per cent by weight of the methylpolysiloxane.

2. The method of rendering leather water repellent comprising contacting the leather with a mixture of siloxanes composed of 50 to per cent by weight of the methylpolysiloxane of claim 1 and up to 50 per cent by weight of a benzene soluble organosilicon compound selected from the group consisting of organopolysiloxanes and organopolysilanes in both of which the organic groups are monovalent hydrocarbon radicals, the aforesaid mixture of siloxanes being employed in a solution of from 1 to 50 per cent by weight concentration of said mixture.

3. The method of claim 2 in which the organic groups of the organopolysiloxanes and organopolysilanes are selected from the group consisting of alkyl and monocyclic aryl radicals.

4. The method of rendering leather water repellent comprising contacting the leather with a solution containing from 1 to 50 per cent by weight of an organosiloxane mixture composed of 50 to 100 per cent by weight of a methylpolysiloxane composed of trimethylsiloxane units and SiOz units in such proportion that the ratio of methyl radicals to silicon atoms is from 1 to 2.5, and up to 50 per cent by weight of a dimethylpolysiloxane fluid.

References fitted in the file of this patent UNITED STATES PATENTS Number Name Date 2,412,470 Norton Dec. 10, 1946 2,441,098 Hyde May 4, 1948 2,462,640 Hyde Feb. 22, 1949 2,469,625 Barry May 10, 1949 2,494,920 Warrick Jan. 17, 1950 2,562,953 Rust Aug. 7, 1951 2,564,674 Cheronis Aug. 21, 1951 2,568,384 Cheronis Sept. 18, 1951 

1. THE METHOD OF RENDERING LEATHER WATER REPELLENT COMPRISING CONTACTING THE LEATHER WITH A SOLUTION OF A METHYLPOLYSILOXANE COMPOSED OF TRIMETHYLSILOXANE UNITS AND SIO2 UNITS IN SUCH PROPORTION THAT THE RATIO OF METHYL RADICALS TO SILICON ATOMS IS FROM 1 TO 2.5, SAID SOLUTION CONTAINING FROM 1 TO 50 PER CENT BY WEIGHT OF THE METHYLPOLYSILOXANE. 